1. Field of the Invention
The present invention relates to a braking device for a motor vehicle, as well as to a method for controlling such a braking device, in particular in cooperation with an autonomous cruise control.
2. Description of the Related Art
Braking devices in motor vehicles are used for selectively decelerating the motor vehicle in the course of a braking operation, i.e., for reducing the velocity of the vehicle, respectively minimizing an increase in the vehicle velocity caused by external influences, such as downhill driving. To this end, a braking device can have brakes that are coupled to the wheels of the motor vehicle and that induce a braking torque on a corresponding wheel, for example, by a pressing of a brake lining against a brake disk. Alternatively to a hydraulic pressing of a brake lining, a braking device can also have brakes in the form of other deceleration mechanisms, such as an electric generator that is coupled to one or a plurality of wheels, for example, and is able to apply a drag torque to the wheel, respectively the wheels, or an eddy-current brake. Typically, each wheel of the motor vehicle is equipped with a corresponding brake. In response to a braking request input by a driver via a brake pedal, for example, the brakes can produce a retarding braking torque on the wheels of the motor vehicle.
Besides the brakes, a braking device in modern motor vehicles includes an open-loop control, respectively a closed-loop control for the open loop, respectively closed loop control of the braking torques that are to be produced by the plurality of motor vehicle brakes in accordance with a setpoint input. This permits individual open loop, respectively closed loop control of the individual wheels, for example, for the braking torques required for an optimum total deceleration of the motor vehicle.
Additionally, during the operation thereof, driver assistance systems, such as an autonomous cruise control, for example, make a targeted selection of desired setpoints for a vehicle deceleration to be implemented and transmit the same to an open-loop control, respectively closed-loop control of a braking device, for example, in order to brake the vehicle independently of a braking request input by a driver, for example, when the vehicle is about to come too close to a vehicle in front.
Braking controls of longitudinal-dynamic functions in a driver assistance system are generally based on a setpoint operated deceleration control. A motor vehicle brake is not actuated until a significant deviation is obtained between a nominal value and an actual value. On the other hand, in the case of such a characteristic curve of controller input variables, the braking torque is reduced to zero, and the brake is completely disengaged during the process, without taking other indicators into account that describe the driving situation.
Instead of a closed-loop control of the deceleration, an open-loop control thereof may also be used where a braking torque to be produced by the braking, that is activated by a trigger, for example, is set to a fixed setpoint value in response to the occurrence of an emergency braking situation.
In connection with driver assistance systems, there are generally prioritization rules that always accord priority to an influencing control by the driver. Such a prioritization of an influencing control executed by the driver routinely leads, for example, to cancellation of an active braking deceleration of the vehicle implemented by a driver assistance system in the course of an autonomous longitudinal control that must be reinitiated following the driver intervention.
It has been noted that specific problems can arise, particularly in the case of braking devices, which, on the one hand, for example, have a setpoint operated open-loop deceleration control, respectively closed-loop deceleration control, to allow an influencing control by a driver assistance system, and which, on the other hand, always accord priority to an influencing control by the driver. In many driving situations, for example, it can happen that implementation of a setpoint controlled braking torque is delayed, and/or that noises that the driver perceives as disturbing can arise which are attributable to a requisite braking pressure being built up for a hydraulic brake, for example.